1. Field of the Invention
The present invention relates to a vibration control of a wind turbine generator.
2. Description of Related Art
Presently, in order to stably generate electric power from natural wind, a wind turbine generator utilizing a horizontal axis wind turbine has been proposed and implemented. Such a wind turbine generator includes a rotor, a nacelle, and a tower. The rotor includes a hub and blades. The nacelle is connected with the hub and supports the rotor through a main shaft extending in an approximately horizontal direction. The tower is disposed in an approximately perpendicular direction and supports the nacelle. In the nacelle a generator connected with the main shaft is provided to compose a wind turbine generator, which generates electric power by converting the rotation energy of the rotor rotated by the wind into electric energy.
In such a wind turbine generator, in order to maintain an appropriate rotation speed of the rotor, electric energy to be taken out from the generator is regularly controlled according to the wind strength.
In this control process, the torque of the rotor may fluctuate and become a vibration source. As the rotor is located on the tower which is elongated and low in rigidity, when the vibration caused by a fluctuation in torque synchronizes with the resonance frequency of the tower, the vibration may develop into a vibration of the entire windmill.
Besides the fluctuation in torque due to rotation control of the rotor, vibration of a windmill is caused by various types of vibrations such as vibration due to Karman vortex generated by the tower, resonance of the speed-increasing gear, the rotor, the generator and the drive axis, and vibration due to bending or torsion of construction.
JP-tokukai-2000-205108 discloses a wind turbine generator with a vibration control device disposed on the top of the tower. The vibration control device has a mass body, a damper device and the like, and the wind turbine generator has a vibration control function to reduce tower vibration.
However, even in the above-mentioned conventional technology, there are problems such as the followings.
The wind turbine generator as recited in the patent document additionally requires a vibration control device, which leads to additional cost. Further, because the vibration control device is to be installed in the tower, it may not be possible to install the vibration control device in a windmill utilizing inside of the tower as a passage leading into an upper part of the windmill. On the other hand, it may not be possible to have a passage inside the tower if the vibration control device is installed.